Method of coating piston ring segments



Jan. 23, 1968 PRASSE 3,364,547

METHOD OF COATING PISTON RING SEGMENTS Filed June 4, 1964 2 Sheets-Sheet1 INVENTQR. Z9 fb efifief 1 1 1 622556 ATTZRNEYS Jan. 23, 1968 H. F.PRASSE 3,364,547

METHOD OF COATING PISTON RING SEGMENTS Filed June 4, 1964 2 Sheets-$heet2 all TTTT I ZLLZLZLL al m] INVENTOR.

WM, @114 1/ W United States Patent Cfifice 3,364,547 Patented Jan. 23,1968 3,364,547 METHOD F COATING PISTON RING SEGMENTS Herbert F. Prasse,Town and Country, Mm, assignor to Ramsey Corporation, St. Louis, Mo., acorporation of Missouri Filed June 4, 1964, Ser. No. 372,473 1 Claim.(Cl. 29--156.4)

This invention relates to coated piston ring segments and to a method ofmaking the same. More particularly, the invention relates to the makingof rail rings, or ring segments, each having a thin, sharp-edged, outercoating of a wear-resistant material to impart to the rings a longereffective life in service.

It has heretofore been known, as in Patent No. 2,905,- 512, to providepiston rings with a wear-resistant, thin coating of molybdenum byspraying molybdenum metal against the outer surfaces of individual ringsmounted on a backing arbor. In accordance with my present invention,however, the rings, or ring segments, are formed from a coil that hasbeen coated with a wear resistant material prior to separation intoindividual rings or seg ments.

Briefly, my method comprises providing a supply coil of a spirally woundelongated strip of a heat-hardenable steel alloy or other suitable metalor alloy, in the form of a relatively thin, fiat ribbon, with the flatfaces of the ribbon in superimposed relationship radially of the coil. Asuitable length of such ribbon is then taken from said supply coil andis rewound into a tightly wound helical coil in which the thin edges ofthe ribbon form the inner and outer surfaces of the coil and the fiatfaces of the ribbon are pressed together into laterally confrontingabutting relationship lengthwise of the coil.

Thereafter, the outer surface of a predetermined length of the coil,While supported edgewise on an arbor, is sprayed to apply to the edgesof the ribbon a thin coating of a wear-resistant material selected fromthe group consisting of molybdenum, tungsten, tantalum and osmium. Afterfiinishing the coated surface, as by abrasion, to the desired thicknessof coating, the turns of the coil are severed lengthwise of the coil toform individual rings or ring segments, each having a transverse gap andeach having the requisite outer and inner dimensions for use in a pistonring assembly.

While the final rings, or ring segments are particularly adapted for useas rail rings in an assembly such as illustrated in the Cable Patent No.2,768,038, the method of my invention is not intended to be limited torail rings only. When used as rail rings, however, the unusually sharplateral edges of the abrasion-resistant coating provided by my methodgreatly enhance the scraping effectiveness of the rings against thecylinder wall without any attendant damage from scuffing the wall assometimes happens with chromium-plated rings.

It is therefore an important object of my invention to provide a new andimproved method for the economical manufacture of piston rings and ringsegments having thin outer edge coatings providing effectivewear-resistant outer surfaces and scraping edges.

It is a further important object of this invention to provide a methodfor making piston rings and ring segments wherein the ring segments areformed from a spirally wound coil of a flat, thin ribbon of a suitablesteel alloy, by winding a length therefrom edgewise into a tightly woundhelical coil of the desired inner diameter dimension, spray coating theouter edge surface of the coil turns with a continuous thin layer of awear-resistant material and severing the coil lengthwise to free theindividual ring segments, each with a transverse gap therein and with anouter, thin, sharp-edged layer of the wear-resistant material.

It is a further important object of this invention to provide pistonrings and ring segments having a thin, sharp-edged outer layer of a highmelting point metal that imparts to the rings and ring segmentsparticularly effective wear-resistant properties while at the same timeimproving their wall-scraping effectiveness in service.

Other and further important objects of this invention will becomeapparent from the following; description of the accompanying drawings,in which like reference numerals refer to like parts, and in which:

FIGURE 1 is a broken, side or end elevational View, partly in sectionillustrating the first step of the method of my invention, wherein alength of the ribbon-like metal strip from which the rings are to bemade, is withdrawn from a spirally wound coil forming a supply of suchstrip, and is rewound edgewise on an arbor into a helical coil of thedesired dimensions;

FIGURE 2 is a side elevational view of the helical coil after removalfrom the arbor of FIG. 1;

FIGURE 3 is a top plan view partly broken away and in section,illustrating a further stage of my method in which the helical coil ofFIG. 2 has been mounted on a supporting arbor and placed under endwiseclamping pressure to facilitate finishing the coil to the desiredoutside diameter dimension, as by grinding or machining;

FIGURE 4 is an enlarged top plan view of the arbor of FIG. 3, or asimilar arbor, also partly broken and in section, illustrating twofurther steps of my method in which the outer surface of the helicalcoil is first sprayed with a wear-resistant material, and then anyexcess of the sprayed layer is removed, as by grinding or machining, toleave a thin coating continuously thereover of the desired finaldimension;

FIGURE 5 is a greatly enlarged fragmentary view, partly in section andpartly in plan, illustrating the steps of severing the helical coillengthwise thereof to form individual rings or ring segments, each witha transverse gap;

FIGURE 6 is a plan view, reduced in size, of a finished piston ringsegment as produced by my method, suitable for use as a rail ring;

FIGURE 7 is an enlarged fragmentary cross-sectional view of a rail ringassembly in a piston ring groove with the piston ring assembly shown inrelationship to the wall of a cylinder in which the piston is operating;and

FIGURE 8 is a fragmentary, perspective view of a mounting of the typewith which my rail ring segments are adapted to be assembled.

As shown on the drawings:

The reference numeral 10 indicates generally a spirally wound coil of anelongated strip 11 of the metal or alloy from which the piston rings orring segments are to be made. Said strip 11 is formed of a thin, fiatribbon having parallel planar surfaces 12 and thin edge surfaces 13 and14. The coil it constitutes a supply coil of an indefinite continuouslength of the strip 11 from which individual lengths of the strip arewithdrawn for processing in the manner about to be described.

Preferably the strip 11 is a strip of a heat-hardenable steel in itsdrawn and. hardened condition. Suitable hardenable steels are thosehaving the specifications S.A.E. 1070 or 1050, but other hardenablesteels and steel alloys can be used. A strip 11 of such drawn andhardened steel is Wound up spirally on a spool 15 with the flat faces 12of the strip in radially superimposed relationship.

In the first step of my method, a length. of the strip 11, beginningwith its free end 11a, is unwound from the spool 15 into a tight helix Hupon a rotatable cylindrical arbor 16 of the proper diameter forimparting to the helically wound strip 11 the desired inner diameter. Asshown, the axes of the spool 15 and the arbor 16 are parallel, therebyrequiring a turning, as at T, of the ribbon in passing from the spoolsto the arbor, but this turning can obviously be obviated by arrangingthe axes at right angles. On the arbor 16 the strip 11 is woundhelically with the flat faces 12 of the turns in laterially confrontingrelationship and with the edge surface 13 forming the outer surface andthe edge surface 14 forming the inner surface of the helix.

After a predetermined length of the strip 11 has been tightly wound onthe arbor 16, a helix of the proper length is cut off, the ends of whichare indicated by the reference numerals 11a and 11b. By uncoiling thehelix slightly, as illustrated by the helix H (FIG. 2) the innerdiameter is increased sufiiciently to permit the helix to be positionedon an arbor 25. When released, the helix will contract to hug the arbor.

The arbor (FIG. 3) may be used as a sizing arbor if the material assupplied requires a grinding or machining operation at this state.Otherwise, this step can be omitted.

Said arbor 25 comprises a driven shaft 17 on the reduced end 18 of whichis mounted, between clamping plates 21 and 23, a cylindrical sizingportion 22. Said sizing portion 22 is of an outside diameter equal tothe desired inside diameter of the finished piston ring or segment, andis of a length slightly less than the length of the helix 24 whencompressed between the clamping plates 21 and 23. Compression lengthwiseof the helix 24 is accomplished by turning up a nut 20 on the threadedportion 19 of the reduced end 18. When fully compressed, the flat faces12 of the helix turns are held pressed together in abuttingrelationship, with the inner edges 14 held tightly against the outersurface of the arbor portion 22 and with the outer edges 13 forming theouter surface of helix 24.

While on the arbor 25, the outer surface of the helix 24 is processed toleave it smooth and fully cylindrical and of an outside diametersubstantially that of the finished piston ring or ring segment whenclosed to circular form. This processing is accomplished by either agrinding or machining operation and is here illustrated as being done bya grinding wheel 26. As indicated above, if not required, this finishingstep can be entirely omitted.

In the next step, with the helix 24 still mounted on the same arbor 25,or on a different but similar arbor, an outer layer of a wear-resistantmaterial is sprayed onto the outer surface of the helix. As illustratedin FIG. 4, a spray gun 27 is used for this purpose. The material sprayedin the manner indicated by the spray 28 is preferably molybdenum butother high melting point, wear resistant metals such as tungsten,tantalum and osmium can be used, as will later be pointed out in greaterdetail. Commercially available spraying equipment, such as that offeredfor sale by Metallizing Engineering Company, Inc., Long Island, NewYork, can be used satisfactorily. The thickness of the coating,indicated by the reference numeral 29, can be controlled to within 0.001inch.

Where such spraying equipment is used, and the metal selected ismolybdenum, the molybdenum is supplied to the spray gun in the form ofwire that is substantially pure molybdenum metal, having a melting pointof about 4750 F. Since the principal oxide of molybdenum is a vapor attemperatures above about 1400 F., the molten material that hits theouter surface of the helix 24 and solidifies thereon to form the layer29 is substantially pure molybdenum metal. As a result, good adherenceof the layer 29 to the surface of the helix 24 is obtained. Said layer29, it should be noted, is continuous over and coextensive with theentire outer surface of said helix 24, and thus bridges the tightlyabutting surfaces between adjacent turns of the helix.

In practice, it has been found advisable to apply a thicker coating ofmolybdenum than that which is to pro vide the desired thinness of thefinal coating on the piston rings or ring segments. Accordingly, if thefinal coating is to be 0.004 inch or less, the initial thickness of thecoating 29 may be in the neighborhood of 0.008 inch and the excess canbe removed by machining or grinding. As illustrated in FIG. 4, theexcess thickness of coating is removed by a grinding wheel 26 or anabrasive belt to leave a final coating 29a of the desired thinness. Thearbor 25 is rotated while the grinding wheel 26 is caused to traversethe length of the helix while being fed radially inwardly into grindingpressure relation therewith.

After the completion of the surface coating and grinding operations, thehelix 24 is next severed lengthwise into individual rings or ringsegments. This severing operation may be performed on the same or on adifferent arbor, but is illustrated as being carried out on the samearbor. For this purpose, the arbor sizing portion 22 has a longitudinalslot 30 extending the full length thereof. Similar slots 31 are formedin the end clamping plates 21 and 23 in alignment with the slot 30.Severing of the turns of the helix 20 is suitably effected by means of athin grinding wheel or diamond disk 32 mounted upon a driven shaft 33.Individual rings, or ring segments 34, are thus formed with gaps 35between their severed ends.

In the act of severing as described, or as a result of the severingoperation in combination with the act of removing the individual rings34 from the arbor 25, the continuity of the coating 29a across thepoints between adjoining turns of the helix 24 is broken to leaveseparate, sharp-edged, thin layers 36 of molybdenum on the respectiveindividual rings 34. Such sharp-edged thin layers of wear-resistantmaterial have better wall scraping properties in service than if suchlayers were formed with rounded surfaces or with surfaces that continuedover the side surfaces of the ring or segment.

Also, molybdenum has been found to be superior to chromium plate as afacing material, since it is higher melting than electroplated chromiumand is less liable to scuff the cylinder wall due to spot seizurebetween the metal of the ring and that of the cylinder wall at hightemperature.

FIGURES 7 and 8 illustrate a typical manner of assembling rail ringssuch as the ring 34, made in accordance with my method. An articulatedassembly ring, such as the expander-spaced ring 37 (FIG. 8), is shown inassociation with rail rings 34 mounted in the oil groove 38 of a piston39 for sealing the piston as it reciprocates within the cylinder 40 ofan engine block 41. For a more complete showing of this type of railring assembly and mounting, reference is made to Patent No. 2,768,038,commonly owned with this application.

As herein described, the high melting point, wear resistant metal usedto coat the ferrous metal rings or segments is one selected from thegroup consisting of molybdenum, tungsten, tantalum and osmium. All ofthese metals have higher melting points than chromium and impartsuperior properties to the rings, or segments, better adapting them fortheir use as piston rings, or segments. In general, the same method thathas been described for molybdenum can be used for spray coating with anyof these other metals, but if tungsten is used, it is preferable tospray the tungsten by a plasma method under nitrogen to preventoxidation.

In the case of a chromium plated rail ring, the edge surface of the railring will be found to be somewhat rounded, due to the fact that theplating continues around the edges themselves. In service, the resultingrounded edge surface tends to cause the rail ring to flop back andforth, much like a paint brush and allows the rail to ride over the oil.Consequently, the ring has an inferior scraping action as compared withthe sharp-edged, metal coated rail rings of my invention. Furthermore,the rail rings herein described afford better oil control because ofbetter sealing. Such better sealing is accomplished without anylocalized concentration of pressure, for the reason that the expandingpressure exerted by the ring against the cylinder walls is moreuniformly distributed than heretofore.

5 I claim as my invention: 1. The method of making piston ring segmentsadapted for use as rail rings, which comprises:

forming a thin, flat ribbon of metal into a helical coil of apredetermined inner diameter,

applying end-wise pressure to said helical coil to press the flat facesof said ribbon into tightly abutting relationship with the thin edgesthereof forming the inner and outer surfaces of said coil,

spray coating the resulting outer surface with a layer of awear-resistant, high melting point metal that is continuous andcoextensive with said outer surface of said helical coil, and thatbridges the abutting thin edges of said ribbon,

removing any excess of said sprayed metal layer to obtain a finalcontinuous layer of predetermined thinness,

severing said helical coil lengthwise thereof, and

freeing the resulting individual ring segments with resultant breakingof said continuous coating layer to obtain ring segments each having atransverse gap and a thin, laterally sharp-edged outer layer of thecoating metal.

References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, PrimaryExaminer. J. S. MEDNICK, Assistant Examiner. LAVERNE D. GEIGER,Examiner.

1. THE METHOD OF MAKING PISTON RING SEGMENTS ADAPTED FOR USE AS RAILRINGS, WHICH COMPRISES: FORMING A THIN, FLAT RIBBON OF METAL INTO AHELICAL COIL OF A PREDETERMINED INNER DIAMETER, APPLYING END-WISEPRESSURE TO SAID HELICAL COIL TO PRESS THE FLAT FACES OF SAID RIBBONINTO TIGHTLY ABUTTING RELATIONSHIP WITH THE THIN EDGES THEREOF FORMINGTHE INNER AND OUTER SURFACES OF SAID COIL, SPRAY COATING THE RESULTINGOUTER SURFACE WITH A LAYER OF A WEAR-RESISTANT, HIGH MELTING POINT METALTHAT IS CONTINUOUS AND COEXTENSIVE WITH SAID OUTER SURFACE OF SAIDHELICAL COIL, AND THAT BRIDGES THE ABUTTING THIN EDGES OF SAID RIBBON,REMOVING ANY EXCESS OF SAID SPRAYED METAL LAYER TO OBTAIN A FINALCONTINUOUS LAYER OF PREDETERMINED THINNESS, SERVERING SAID HELICAL COILLENGTHWISE THEREOF, AND FREEING THE RESULTING INDIVIDUAL RING SEGMENTSWITH RESULTANT BREAKING OF SAID CONTINUOUS COATING LAYER TO OBTAIN RINGSEGMENTS EACH HAVING A TRANSVERSE GAP AND A THIN, LATERALLY SHARP-EDGEDOUTER LAYER OF THE COATING METAL.